1. Field of the Invention
The present invention relates to ultrasonic microscope systems used in the analysis of the properties of solid samples and, more particularly, to an improved acoustic microscope system.
2. The Prior Art
A well known acoustic microscope employed by many researchers uses a cylindrical lens in a "V(z)" scan technique, wherein V(z) represents the voltage amplitude of the transducer output signal as a function of the normal distance, i.e., the distance measured along the z axis, between the transducer and the sample being analyzed. This technique or approach, hereinafter referred to as the Kushibiki system, is discussed, for example, in Jun-Ichi Kushibiki and Noriyoshi Chubachi, "Material Characterization by Line-Focus-Beam Acoustic Microscope," IEEE Trans. on Sonics and Ultrasonics, Vol. SU-32, No. 2, 189-211, March 1985, and is the basis of at least one commercial acoustic microscope system, viz., the Honda AMS 5000 Ultrasonic Measuring System. In the system discussed in the cited reference, the transducer includes a polished sapphire lens having a concave cylindrical front surface. The active piezoelectric element, i.e., the element which converts elastic changes into an electrical output as a receiver, and converts electrical input into elastic wave motion as a transmitter, is a flat ZnO film provided on the back side of the lens. The transducer is operated in a burst continuous wave (CW) mode. The most important measurement made by this system is that of the scan distance z. More specifically, in this method, precise z distance control and measurement are necessary in order to determine the distance between two maxima or minima in the V(z) curve (i.e., the plot of V as a function of distance z) and to compute the speed using the known CW frequency. The signal processing used is a gated voltage measurement made as the transducer is moved in the z-direction. Fourier transforms are necessary to convert the V(z) curve into the desired velocity values.
Patents in the field which were of interest include the following: U.S. Pat. No. 4,510,810 (Kanda et al.); U.S. Pat. No. 4,541,281 (Chubachi et al.); U.S. Pat. No. 4,566,333 (Chubachi et al.); 4,577,504 (Kanda et al.); U.S. Pat. No. 4,597,293 (Kanda et al.); U.S. Pat. No. 4,603,585 (Atalar); U.S. Pat. No. 4,655,083 (Chubachi); U.S. Pat. No. 4,694,699 (Cheeke); U.S. Pat. No. 5,211,059 (Hayakawa et al.); U.S. Pat. No. 5,307,680 (Drescher-Krasicka); and U.S. Pat. No. 5,349,862 (Chubachi et al.).
Briefly considering these references, the Kanda et al. ('810) patent discloses an ultrasonic microscope which uses a flat piezoelectric element located on top of an acoustic lens. The Chubachi et al. ('281 & '333) patents discloses an ultrasonic microscope system which uses a flat piezoelectric element disposed over a curved acoustic lens. The Kanda et al. ('504) patent discloses an ultrasonic transducer with a piezoelectric element disposed over an acoustic lens. The Kanda et al. ('293) patent discloses mounting a piezoelectric element on the concave bottom surface of a substrate such that the piezoelectric element is likewise curved in shape. The Atalar patent discloses a flat piezoelectric element mounted on top of an acoustic lens. The Chubachi ('083) patent discloses dual transducers with piezoelectric elements located on top of acoustic lenses. The Cheeke patent discloses an acoustic microscope transducer comprising a cylindrical lens with a piezoelectric element mounted on top of the lens. The Hayakawa et al. patent discloses an acoustic microscope transducer comprising multiple piezoelectric elements mounted on the bottom curved portion of an acoustic lens. The Drescher-Krasicka patent discloses an acoustic microscope transducer which utilizes a curved acoustic lens. The Chubachi et al. '862 patent discloses an ultrasonic microscope in which circular shaped piezoelectric elements are mounted on the flat top of an acoustic lens.